As is known, physicians rely heavily on their ability to use tactile feedback during a clinical breast examination (CBE) in order to determine the presence of lumps, nodules and other tissue abnormalities that might be indicative of breast cancer. These types of examinations often include soft and hard presses of tissue to feel depth and palpations and squeezes of the tissue to feel the extent of the tissue's, mass. Hence, in order to properly tram medical residents to conduct a CBE properly, training systems incorporating touch sensing technology have been developed.
As is known, touch sensing technology is used in a variety of electronic products, including medical devices. In these types of training systems, it is highly desirable for the sensor to have the ability to track normal pressure exerted by a force, as well as, the direction and locus of movement of the force. For example, the force may take the form of a hand of the physician during examination of a breast. However, current sensing solutions available to physicians are based on piezoelectric sensing schemes and are capable of measuring only normal pressure over a large area, but not directional changes. As a result, the sensors in current training systems are incapable of tracking motions, e.g. circular motions, which are critical to determine the size of a lump. Further, these sensors in current training systems also show hysteresis and are susceptible to drift due to temperature variations and external vibrations.
In order to overcome the challenges associated with piezoelectric sensing schemes in current naming systems, the use of capacitive touch sensor technology has been explored. A capacitive sensing solution is preferred because of its high sensitivity, low power consumption and low drift. Prior work in the area of flexible capacitive sensors has mainly focused on the electrode design for robotic tactile sensing. These capacitive sensors utilize a thin layer of an elastomer, e.g. polydimethylsiloxane (PDMS) or Ecoflex, as a dielectric layer, whose compression allows for the limited measurement of normal forces, and displacement allows for the measurement of shear to some extent. Deformation of an elastomeric thin film subjects the types, of capacitive sensors to intrinsic mechanisms, which results in long relaxation times after compression.
Therefore, it is a primary object and feature of the present invention to provide a flexible, three-axis, capacitive touch sensor that is capable of resolving normal pressure to and tracking directional motion.
It is a further object and feature of the present invention to provide a flexible, three-axis, capacitive touch sensor that deforms easily and allows for a quick recovery from the deformation so as to improve the sensitivity thereof.
It is a still further object and feature of the present invention to provide a flexible, three-axis, capacitive touch, sensor that is simple and inexpensive to manufacture.
In accordance with the present invention, a capacitive touch sensor is provided. The capacitive touch sensor includes a plate having an upper surface and lying in a plate plane. A generally planar, first electrode is spaced from the plate along an axis generally perpendicular to the upper surface of the plate. The first electrode movable with respect to the plate in response to a force. A plurality of second electrodes are interconnected to the plate and circumferentially spaced about the axis. Each of the plurality of the second electrodes having a corresponding differential capacitance with the first electrode. The differential capacitances between the first electrode and the plurality of second electrodes vary in the response to the movement of the first electrode.
A dielectric layer extends between the plate and the first electrode and includes a plurality of dielectric posts. The dielectric posts flex in a direction corresponding to a direction of the force applied to the first electrode. Each of the plurality of second electrodes is generally flat and lies in an electrode plane generally parallel to the plate plane. Each of the plurality of second electrodes has a generally square configuration. At least a portion of the first electrode is moveable in an x-direction, a y-direction and a z-direction, wherein: the y-direction is generally parallel to axis; the x-direction is generally perpendicular to the y-direction; and the z-direction is generally perpendicular to the x-direction and the y-direction.
In accordance with a further aspect of the present invention, a capacitive touch sensor is provided. The capacitive touch sensor includes a plate lying in a plate plane having a first set of electrodes supported on an upper surface thereof. Each electrode of the first set of electrodes is circumferentially spaced about an axis extending through the plate and is perpendicular to the upper surface. A generally planar, first electrode is spaced from the plate along the axis. The first electrode is movable with respect to each electrode of the first set of electrodes in response to a force and has a corresponding differential capacitance with each electrode of the first set of electrodes. The differential capacitances between the first electrode and each electrode of the first set of electrodes varies in the response to the movement of the first electrode.
A dielectric layer extends between the plate and the first electrode, and includes a plurality of dielectric posts. The dielectric posts flex in a direction corresponding to a direction of the force applied to the first electrode. Each electrode of the first set of electrodes is generally flat and lies in an electrode plane generally parallel to the plate plane. Each electrode of the first set of electrodes has a generally square configuration. At least a portion of the first electrode is moveable in an x-direction, y-direction and a z-direction, wherein: the y-direction is generally parallel to axis; the x-direction is generally perpendicular to the y-direction; and the z-direction is generally perpendicular to the x-direction and the y-direction.
In accordance with a still further aspect of the present invention, a method of tracking pressure exerted by and a locus of movement of a force is provided. The method includes the step of exerting a pressure on a sensor with the force. The sensor has a variable differential capacitance. The differential capacitance is varied in response to at least one of the pressure exerted by the force on the sensor and a locus of movement of the force along the sensor.
The sensor includes a plate having an upper surface and lying in a plate plane. A generally planar, first electrode is spaced from the plate along an axis generally perpendicular to the upper surface of the plate. The first electrode is movable with respect to the plate in response to a force. A plurality of second electrodes are interconnected to the plate and are circumferentially spaced about the axis. Each of the plurality of the second electrodes has a corresponding differential capacitance with the first electrode. The differential capacitances between the first electrode and each of the plurality of second electrodes vary in response to at the pressure exerted by the force on the first electrode and/or in response to the locus of movement of the force along the first electrode.
The sensor also includes a dielectric layer extending between the plate and the first electrode and includes a plurality of dielectric posts. The dielectric posts flex in a direction corresponding to at least one of the pressure exerted by the force on the first electrode and the locus of movement of the force along the first electrode. At least a portion of the first electrode is moveable in an x-direction, a y-direction and a z-direction, wherein: the y-direction is generally parallel to axis; the x-direction is generally perpendicular to the y-direction: and the z-direction is generally perpendicular to the x-direction and the y-direction.